The long-term goal of this research program is to understand the hydration of nonpolar and polar solutes in aqueous solutions. We will use computer simulations, based on the Monte Carlo and molecular dynamics methods, to study the structure of liquid water and the structural changes that take place on introduction of one or more solute molecules or ions into the liquid. First, we will try to develop simulation methods that are ten to one hundred times more efficient than those that have been used to study water and aqueous solutions. Several suggestions for achieving this increase in efficiency are discussed in detail in the proposal. Secondly, we will simulate solutions of one or more nonpolar solutes, polar solutes, and ions in water, to understand such processes as hydrophobic hydration, hydrophobic interaction, the "salting out" effect, and ion pairing. Thirdly, we may simulate more complicated processes, such as the interaction of water and ions with membrane surfaces and with chemical reactions.